In the field of vehicle control, stability refers to the ability of a vehicle to maintain its intended course. Under certain circumstances, a vehicle may become unstable, meaning that the vehicle deviates from its intended course and/or is no longer able to maintain body (longitudinal, lateral, yaw, roll) control. Loss of stability may be caused by forces associated with cornering and accelerating-braking. The ability of the vehicle to maintain stability is in part a function of the friction available at the surface on which the vehicle is travelling. For example, braking and cornering require more available friction than straight line driving at constant speed, and the vehicle may become unstable when the friction required by a cornering or braking maneuver exceeds the available friction.
Electronic stability control systems are intended to detect and reduce loss of directional stability. Conventional electronic stability control systems determine a steering direction by measuring the steering wheel angle, and estimate the vehicle's intended course based on the vehicle states, such as, lateral acceleration, yaw, and road wheel speeds. The electronic stability control system may determine that the vehicle has lost stability based on a deviation of the vehicle's actual measured states, such as yaw rate direction from the estimated intended course. Upon determining that the vehicle has lost stability, the electronic stability control system can apply braking at the road wheels individually and/or request propulsion torque to regain stability. For example, braking may be applied to the outer front wheel to counter oversteer or braking may be applied to the inner rear wheel to counter understeer.